The freshman congressman has scheduled an event Tuesday with supporters in his hometown of Dardanelle. A person who has spoken with Cotton said the congressman intends to enter the race against Pryor, who faces re-election next year.

The person who spoke to The Associated Press on Wednesday was not authorized to speak publicly about the planned announcement and spoke on a condition of anonymity.

Cotton was elected to the U.S. House in 2012, to the open seat formerly held by Democrat Mike Ross. Ross is now running for Arkansas governor.

Cotton, 36, is a former management consultant who served in the Army in Iraq and Afghanistan. He was elected to the 4th District in November, after racking up endorsements during his primary bid from national Republican leaders including U.S. Sen. John McCain of Arizona and conservative groups such as the Club for Growth.

The Club for Growth in February launched the first television ad against Pryor, seen by many as a signal that the group would back Cotton's potential candidacy.

Pryor is viewed by many Republicans as the most vulnerable Senate incumbent next year, especially after recent GOP gains in Arkansas. Republicans in November took over the state Legislature for the first time since Reconstruction and swept all four of the state's U.S. House seats.

Republicans are trying to unseat Pryor and three other Democratic incumbents who represent states that Republican Mitt Romney won in last year's presidential race: Mark Begich of Alaska, Kay Hagan of North Carolina and Mary Landrieu of Louisiana.

Democrats need to defend 21 seats, including seven in largely rural states that Obama lost in 2012.

Republicans need to pick up six seats to regain Senate control.

On Wednesday, Pryor's campaign wasted no time in hitting back, accusing Cotton of alienating constituents on issues ranging from farming to Social Security.

"Instead of putting Arkansas first, he has put his own political career ahead of the people of Arkansas and sided with Washington insiders and special interests," Pryor's campaign manager, Jeff Weaver, said in a statement. "When the people of our state review Tom Cotton's record, they won't like what they see."

Groups on the right and left have already been airing ads throughout the state targeting Pryor. A gun control group founded by New York Mayor Michael Bloomberg has aired spots criticizing the Democratic lawmaker for voting against expanded background checks. Pryor used his first TV spot to defend his vote against the criticism.

Since taking office in January, Cotton has enjoyed a high profile with multiple appearances on national programs such as Meet the Press. Cotton in July wrote a column for the Wall Street Journal opposing Senate immigration legislation.

He's also been targeted by Democrats who viewed him as a likely challenger to Pryor. Two Democratic political action committees, Patriot Majority USA and Senate Majority PAC, launched a $270,000 television ad buy in June attacking Cotton for allegedly seeking the national spotlight at the expense of his district.

State Democrats continued that criticism of Cotton on Wednesday.

"Today's announcement proves that Tom Cotton's number one priority in his first few months as a congressman has been to further his own political ambition over the needs of his constituents," spokeswoman Candace Martin said in a statement released by the party.

Cotton has faced criticism from Democrats for initially opposing the farm bill over objections to the food stamp program. Cotton later voted for a version of the farm bill that did not include funding for food stamps.

Cotton's also come under fire for a recent proposal that would have extended sanctions on Iranian human rights violators to their families — an idea that has been criticized as eliminating due process. Cotton, who withdrew the proposal, has defended the idea and said it would only apply to sanctions on Iranians, not any American citizens.

Cotton's appeal to conservative activists stems from his resume as a Harvard-educated veteran who's known for his rhetorical flourishes.

When he joined with House Republicans to vote for the federal health overhaul's repeal, he compared the unsuccessful effort to defeat the law to an ancient Roman senator's ongoing call to destroy Carthage. When Venezuelan President Hugo Chavez died in March, Cotton responded with "Sic semper tyrannis," or Latin for "thus always to tyrants." John Wilkes Booth uttered the same after assassinating President Lincoln.

Cotton's candidacy will likely have a domino effect on other races in Arkansas. House Majority Leader Bruce Westerman plans to seek the Republican nomination for Cotton's seat and will formally launch his campaign in August, a person who had spoken to the lawmaker told the AP. The person spoke on condition of anonymity because Cotton had not yet formally launched his Senate campaign.

Lt. Gov. Mark Darr has said he'd likely run for Cotton's seat if the congressman ran for Senate. Janis Percefull, a community college teacher, is the only Democrat running for the 4th District seat.

Unfortunately, he doesn't have the experience or education to make a good Senator. He's just a pretty face for the Republican media machine.

Instead of authoring bills, he rubber stamps them and votes with the majority. Where is the leadership (no, the "Army" doesn't really count), experience as a "Management Consultant" ? Really, that's a very vague description for basically doing nothing.

And jumping ship after less than one 2 year term makes me very uncomfortable with his commitment.

He's young and pretty, and maybe in 20 years he'll have the qualifications for a US Senator. Not yet . . .